In a dipping type phosphating system, an object to be treated is introduced into a bath containing a phosphating liquid, so that the object is fully dipped into the fluid. In such a system, the formation of a film layer of the phosphate crystals on the surface of the object after the treatment is mainly determined by a chemical reaction between the object and the liquid which takes place in a time period, for instance, as short as 0.5-30 sec. from the beginning of the dipping of the object in the liquid. However, when the object has a complicated configuration, the liquid does not uniformly reach all portions in such a short time period, so that air-pockets are apt to be generated. Such air-pockets adversely affect the corrosion resistibility during use.